1. Field of the Invention
The present invention relates to the field of fuel injectors, and more particularly to intensifier type fuel injectors.
2. Prior Art
Intensifier type fuel injectors are well known in the prior art. As an example, see U.S. Pat. No. 5,460,329. That patent discloses an electromagnetically actuated spool valve for controlling the coupling of an area over an intensifier piston to an actuating fluid under pressure or to a vent, the intensifier piston driving a smaller piston to intensify the pressure of fuel for injection purposes. While various types of valves are known for use with such injectors, the valves generally control the flow of actuation fluid to and from the area over intensifier piston.
While control valves of the foregoing type can be made relatively small and fast-acting, control of actuation fluid in this manner for direct fuel injection has certain limitations. In particular, a diesel fuel injector may intensify fuel pressure to a pressure on the order of 20,000 psi or higher, at which pressures the fuel will undergo substantial compression. This, in turn, means that there must be substantial actuation fluid flow into the chamber over the larger piston of the intensifier. In that regard, while, by way of an example, in an intensifier having an area ratio of 9:1, the pressure of the actuating fluid over the larger piston will only be 1/9 of the intensified pressure, the flow of actuation fluid required to achieve the compression and intensification of the fuel will be nine times that required because of the compression of the intensified fuel, thereby resulting in at least as much volumetric compression in the actuation fluid over the intensifier piston as in the intensified fuel. Consequently, intensification on actuation of the control valve(s) requires significant actuation fluid flow, and is therefore less than immediate. Also, this flow requirement sets the minimum size for the electrically operated control valves, and further requires de-intensification between injection events, making multiple injections during a single injection event difficult and energy consuming.